change string view to spdlogs, remove bool type

include/spdlog/details/log_attr.h

@@ -11,7 +11,7 @@ namespace details {
 
 template<typename T>
 struct is_string
-    : public std::integral_constant<bool, std::is_convertible<T, std::string>::value || std::is_convertible<T, std::string_view>::value>
+    : public std::integral_constant<bool, std::is_convertible<T, std::string>::value || std::is_convertible<T, string_view_t>::value>
 {};
 
 template<typename T>
@@ -37,12 +37,6 @@ public:
         : key(std::string(k))
         , value(std::to_string(v))
     {}
-
-    template<typename key_t, typename std::enable_if<is_string<key_t>::value, key_t>::type * = nullptr>
-    attr(key_t const &k, bool const v)
-        : key(std::string(k))
-        , value(v ? "true" : "false")
-    {}
 };
 
 } // namespace details